1. Field of the Invention
This invention relates to volumetric pumping apparatus and method for the precisely controlled and coordinated supply of sheath stream and sample fluids to a sheath stream flow cell for sample analyses; particularly as adapted for high-speed automated biomedical analytical systems.
2. Description of the Prior Art
Although prior art apparatus and methods are known for the supply of sheath stream and sample fluids to sheath stream flow cells, none are known to applicant which can accomplish these functions in the precisely controlled and coordinated manner provided by the teachings of this invention.
In many instances these prior art apparatus and methods utilize peristaltic pumping to supply the sample fluid stream to the flow cell. This is disclosed, for example, in U.S. Pat. No. 3,740,143, wherein peristaltic pumping is used to supply a series of diluted blood samples to a sheath stream flow cell for white blood cell differentiation and counting, and has now been determined in accordance with the teachings of this invention to lead to less than optimal accuracy in cell differentiating and counting due to marginal variations in peristaltic pump roller and pump tube dimensions, which cause variations in the diameter, velocity and/or volume of the sample fluid stream through the flow cell. Since separate pumping systems are used (the sheath stream fluid is pressure pumped from a constantly pressurized source in U.S. Pat. No. 3,740,413), variations in the essential sheath-sample fluid streams flow and volume ratios can also occur to further degrade sample analysis accuracy. In addition, peristaltic pumping requires frequent and precise calibration; while the relatively long lengths of peristaltic pump and supply tubing markedly increase the potential for sample carryover. Carryover is defined as the contamination of a succeeding sample by the residue of a preceding sample resulting in loss of accuracy. Further, peristaltic pumping, which operates by the occlusion or squeezing of the pump tubes by the pump rollers, can and does result in damage to the integrity of cells or like sample fluid particles to further degrade accuracy.
Although more current efforts have been made to remedy some of the above-described problems through utilization of separate, finely calibrated peristaltic pumps for each of the sheath stream and sample fluids as described, for example, in paper HYDRODYNAMICS OF CONCENTRIC PERISTALTIC LAMINAR FLOW OF TWO DIFFERENT FLUIDS by applicant and I. Beretsky, M.D., presented at the Mar. 23, 1973 meeting of The American Association For Medical Instrumentation at Chicago, Ill., these efforts have not proven fully satisfactory, especially in increasingly sophisticated automated biomedical analytical systems.
Other apparatus and methods are known for the supply of sheath stream and sample fluids to a sheath stream flow cell and, as disclosed in U.S. Pat. No. 3,661,460, use a combination of gravity feed, peristaltic pumping and vacuum pumping, requiring liquid trap, pressure regulation, pressure gauge, and needle valve or other flow restrictor means, to those ends. These apparatus and methods can be difficult to calibrate and tend not to remain calibrated.
In unrelated fields of endeavor, double-acting reciprocating pumps having different effective pumping capacities are exemplified by U.S. Pat. Nos. 2,025,142, 2,163,607, 3,205,825 and 3,713,755 wherein such pumps are disclosed in conjunction with the cooling of gas compressors, the bellows pump-proportioning of high-pressure fluids, the proportioning of fluids for beverage dispensing, and the thrust piston motor means-driven conveyance of fluids, respectively.
Clearly, none of these uses is relevant to the teachings of this invention, which particularly adapt the basic concepts of differential, double acting pumping to the precisely controlled and coordinated supply of sheath stream and sample fluids to a sheath stream flow cell.